The twenty-first sutra states about the elusive power of the yogi, who possesses the capability to make himself invisible from the observers. He also has the power to vring himself back to ordinary perception.

kaya body
rupa form
samyamat constraint, control
tad from that form
grahya to be seized, taken, received, perceivable
lakti power, capacity, emanation
stambhe suspension
caksuh eye
prakasa light
asamprayoge there being no contact
antardhanam disappearance, invisibility

By control over the subtle body, the yogi can suspend at will the rays of light radiating from himself, so that he becomes invisible to onlookers. He may again make himself visible by bringing back the power of perceptibility.